1Put the flour and sugar and a pinch of salt in a bowl, mix, add the diced butter and egg and mix until you get a ball of smooth dough.
2Wrap in plastic and refrigerate for 2 hours.
3Remove the dough from the refrigerator, allow to sit for 10 minutes to warm up a bit before rolling out on a floured surface.
4Place the dough into a lightly buttered springform pan.
5Cut edge with a sharp knife.
6Preheat the oven at 350F.
7Separate the eggs, discard 2 yolks, or reserve them for later use.
8Combine cream cheese, butter, cream and half the milk in a saucepan.
9Heat over medium heat and bring to a boil.
10Meanwhile, in a medium bowl, mix the yolks with the remaining milk, vanilla, lemon zest and flour. Once the cream cheese mixture boils, slowly add the egg yolk mixture. Cook over low heat for about 5-7 minutes.
11(It will have the consistency of a thick english cream, but not as thick as custard).
12Set aside to cool.
13Beat the egg whites until stiff peaks form, then gradually add the confectioner's sugar.
14Stir 2 tablespoons of egg whites into the cream cheese mixture, to lighten it up a little bit.
15Then gradually add the remaining egg whites, gently folding with a rubber spatula so that it does not break.
16Pour the batter into the pan and smooth the top (don't fill the mold up to the top, leave 1 cm since it will rise).
17Bake for 30 minutes to 350 C then bake 15 to 20 minutes more at 250 C.
18Let it cool in the oven until it is almost cold, then cool on a wire rack for 10 minutes to prevent the filling from sinking.
19Unmold on a serving dish, sprinkle with confectioner's sugar.